Thermoresponsive cable



Patented Oct. l5, 1946 THERMORESPONSIVE CABLE Richard D., Kaul, Fairfield, Conn., assigner to Ther Sealand Corporation, Southport, Conn., a corporation of ComlcQticut Application August 17, 1943, Serial No. 499,000

Claims. 1

This invention relates t0 improvements in thermo-responsive cable.

It is the general object of the invention to provide an improved thermo-responsive cable for indicating fire or other high temperature con` ditions.

A specic object of the invention is to provide a cable in which the certainty of response to the temperature condition to be indicated is increased.

A second specific object of the invention is to provide a cable construction which reduces impairment of response or dielectric strength by deterioration of the cable structure due to iiexure or other mechanical abuse.

The cable of the present invention constitutes an improvement upon that disclosed in Lindsey Patent No. 2,048,271, granted July 2l, 1936, the general purposes and functions of the cable being similar.

With the foregoing objects, as well as others which will appear in the following full description in mind, the invention consists in the combinations and arrangements of parts and details of construction which will now first be fully described Yin connection with the accompanying drawing and then more particularly pointed, out in the appended claims.

In the drawing:

Figure 1 is a perspective View of a section of cable embodying the invention in a preferred form and with the elements progressively removed so as to show the internal structure;

Figure 2 is a perspective View showing the center conductor member of the cable of Figure 1; and

Figures 3 and 4 are typical cross sections, upon an enlarged scale, taken at different points along the length of the cable of Figure l.

The cable elements, as shown in Figure l, include a fusible alloy core A, contained Within a seamless copper tube B, forming an inner conductor and having apertures b to permit the.

alloy to fiow or spurt out upon melting. The tube B is covered by a winding C of insulating material, and a second seamless copper tube D, which -forms an outer conductor, is drawn onto the insulating winding C. As in the Lindsey patent, above referred to, the cable will be located so as to indicate re or other conditions causing temperature rises, the inner and outer conductors B and D being included in an alarm circuit which is completed upon fusing of the alloy core A which connects conductors B and D by means of the fused alloy passing through one .or more of the apertures b. Such alarm circuits, aswell as auxiliary connectors and ttings for use with fire detecting cable, being well known and forme ing no part of the present invention, will not; be further referred to.

For indicating fires, a fusing temperature of about F. is generally suitable, and the core A may be made of Woods metal or Lipperwitzs metal. The invention, however, is not conned to the indication of a specic temperature or condition but may be applied to indicating any desired temperature, an alloy Aor metal with a suitable melting point being selected.

In manufacturing the cable in the preferred form, an oversize tube B is drawn down onto the core A so as to t the same closely or compressively and eliminate all voids, so far as possible, with a View to compelling the alloy, when melted, 4to spurt through an aperture b. The apertures b are spaced along the tube B as indicated in Figure 2, so as to weaken the tube B as little as possible, and in addition are preferably made in the form of narrow slots, which may conveniently be formed by slitting or punching the metal of tube B after drawing the same down on the core A and then pressing the edges of the slit back together. While it will be understood that the specific dimensions may be widely varied, in the example selected for illustration, slits b approximately one-quarter inch long and spaced longitudinally of the cable at three inch intervals have been found satisfactory in a cable having an overall outside diameter of slightly over one-eighth inch. Before applying the insulating layer C, a coat of insulating lacquer or varnish is preferably applied to the tube B. The insulating layer C may be of any suitable insulating material, and of any suitable form so long as it will permit the molten alloy to pass through it; in the embodiment shown, a wrapping of beeswax-impregnated cotton or paraffin-impregnated cotton has been found satisfactory. As indicated above, manufacture is completed by drawing down an oversize tube D so as to i'lt tightly upon the insulating layer C. Figure 3 of the drawing shows the completed cable structure in typical cross section passing through an aperture b, and Figure 4 is a typical cross section at a point where there is no aperture b.

The advantages of the present invention will be best understood by referring to significant points of difference between the present construction and that of the Lindsey patent, above referred to.

By employing separate apertures b, instead of a continuous slot, in the inner conductor B, the expansive force of the melting alloy core A is conned and results in a more positive flow or spurt of alloy through the apertures. Secondly, the use of a ductile and highly conductive metal, such as copper, is. made possible, as it is unnecessary to use a steel or iron conductor B in order to obtain the required strength, which is the case when a continuously slotted conductor is used. The ductility and continuity of the inner conductor B make it possible for the cable to withstand considerable bending or other mechanical abuse without creating undue voids around the core A or otherwise impairing the cable, While, as is apparent, a continuously slotted conductor cannot be bent Without gaping and creating voids.

What is claimed is:

1. A thermo-responsive cable comprising inner and outer tubular conductors, insulating material between said conductors and a core of fusible conducting material within the inner conductor, the said inner conductor having longitudinally spaced apertures but having an otherwise continuous Wall.

2. A thermo-responsive cable comprising inner and outer tubular conductors, insulating material between said conductors and a core of fusible conducting material Within the inner conductor, the said inner conductor comprising a seamless tube drawn onto said core and having longitudinally spaced apertures.

3. A thermo-responsive cable comprising inner and outer seamless metal tubes, insulating material between said metal tubes and a core of fusible conducting material within the inner tube, the said inner tube having longitudinally spaced apertures but having an otherwise continuous wall.

4. A thermo-responsive cable according to claim 3, in which the said inner tube is drawn down onto said core in compressing relation thereto.

5. A thermo-responsive cable according to claim 3, in which said inner and outer tubes are respectively drawn down onto said core and said insulating material in compressing relation thereto.

RICHARD D. KAUL. 

